A fluid flow control valve in one form comprises a solenoid structure for selectively positioning a valve member. The solenoid structure includes a solenoid coil retained in association with a solenoid tube. An armature is slidably received within the tube for selective positioning as an incident of selective energization of the solenoid coil.
A typical spool type cartridge valve includes a valve body having a valve chamber with a select number of ports. A valve spool is slidably mounted in the valve chamber for controlling flow between ports. The valve spool is slidably connected to the armature.
In a two position spool type valve, the spool and armature are biased in one position, as by a coil spring. The solenoid when energized develops a sufficient magnetic field to cause the armature to overcome the force of the spring and thus move the spool to an actuated position.
With a three position solenoid valve, the valve includes a pair of solenoids. The spool is biased to a neutral position by means of one or more springs. The pair of solenoids act on one or more armatures to selectively push or pull the armature, and thus the spool, to move the spool from the neutral position to one of two opposite actuated positions, thus the name three position solenoid valve.
A typical three position valve in one form includes a single armature within a brazed tube. Specifically, the armature is mounted between a closed inner end and an insert positioned in the outer end of the tube to create two stop positions for the armature. Indeed, the insert and closed ends define the limits for axial movement of the armature and thus define a pair of opposite full and equal substrokes for movement of the armature, and thus also the spool. The coil spring is used to maintain the armature, and thus the spool, in a neutral position with the armature centered between the two stop positions.
It has been found that the use of an insert results in a loss of force which might otherwise be exerted on the spool. Specifically, the flux path developed by the solenoid through the tube must overcome the air gap between the solenoid coil and the insert, resulting in force losses which might otherwise be used for actuation.
Further, a necessity of using the insert causes the tube to be longer than is required for the armature.
The present invention is directed to overcoming one or more of the problems set forth above in a novel and simple manner.